External frame backpacks are particularly well suited for carrying heavy, bulky loads by backpackers. The load is carried a small distance away from the back of the user and is secured to a rigid frame that can transmit the load primarily to the hip belt. However, with conventional frames and hip belts, the load is not effectively transferred to the sides of the hips, the location most comfortable over a long haul. Instead the load is mainly carried on the small of the back as the hip belt sags and pulls from behind.
Some attempts at overcoming this loading have been made by the use of straps and other equipment. For example, one attempted solution employs T-shaped arms rigidly secured to the frame rails and extending forwardly to an attachment with the sides of the hip belt. This arrangement will transfer the load to the sides of the user's hips, but may also cause the pack to shift or swing side to side with every natural hip movement of the user. The connection is kept somewhat rigid for effective transfer of the load to the user's hips.
Other problems with external frame pack harnesses involve the back and lower panels that are used to suspend the pack frame away from direct contact with the user's back. These panels are strapped to the siderails of the pack and held in tension horizontally. They may, therefore, develop horizontal wrinkles or folds that feel uncomfortable on the back of the user. Furthermore, the load may not be effectively and evenly distributed across these panels for a comfortable carry.
Owing to the limitations of the current external frame packs, the advantages of these packs as effective big-load haulers is overshadowed. Therefore, a need exists for a rigid external frame pack with a flexible harness system that effectively carries a load comfortably on the user's back with the bulk of the downward force transferred to the sides of the hips of the user without pack instabilities being created when hiking.